Two-speed motor drive with positive stop



June 6, 1950 H. B. FUGE TWO-SPEED MOTOR DRIVE WITH POSITIVE STOP FiledSept. 8. 1948 MS'ITIVE STOP TORQUE grvve-nboz/ Harry 5- u/ye w dtt'onwyPatented June 6, 1950 TWO-SPEED MOTOR DRIVE WITH POSITIVE STOP Harry B.Fuge, Somerviile, N. J., assignor to The Singer Manufacturing Company,Elizabeth, N. J., a corporation of New Jersey Application September 8,1948, Serial No. 48,214

7 Claims.

tern of electrical braking involving a new and useful combination ofmotor elements and control units.

It is, therefore, a primary object of this invention to provide a motorcontrol system in which the act of stopping is preceded by a reductionof the motor speed to an intermediate value by operating said motor atsupersynchronous speeds to effect braking by absorption of therotational energy as an induction generator.

A further object of this invention is to provide a simple motor systemfor controlling a machine throughout an operating cycle, includingacceleration, deceleration and positive step of the driven machine at apredetermined point in the cycle without the use of clutches.

A still further object of this invention is to provide a squirrel-cageinduction motor which may be readily braked from high speed to lowspeed, said low-speed connection being productive of zero torque atstandstill.

A further object of this invention is to provide a method of stopping amotor driving an inertia load by electrically braking said motor to anintermediate speed and subsequently driving into a positive stop at lowspeed.

With the above and other objects in view, as will hereinafter appear,the invention comprises the devices, combinations, and arrangements ofparts hereinafter set forth and illustrated in the accompanying drawingsof a preferred embodiment of the invention, from which the severalfeatures of the invention and the advantages attained thereby will bereadily understood by those skilled in the art.

In the drawings, Fig. 1 is a schematic wiring diagram of a motor controlsystem embodying the invention.

Fig. 2 shows the torque-speed relations involved in the motor of Fig. 1.

Referring to Fig. 1, a motor I, preferably a squirrel-cage inductionmotor, is shown as com prising a polyphase stator winding 2 and aseparate single-phase winding 3. The single-phase winding has more polesthan the polyphase winding and thus provides a stator field of lowersynchronous speed. Preferably, but not necessarily, the single-phasewinding 3 has twice as many poles as the polyphase winding 2. A machine39, connected to be driven by the motor I, is adapted to drive into apositive stop at the completion of a definite work cycle. Machines ofthis type are well known, one being shown and described, for example, inU. 8. Patent No. 542,196, July 2, 1895, to which reference may be hadfor a detailed description thereof.

A normally-open contactor 5, having contacts 6, l, 8 and an operatingcoil 9, is employed to connect the polyphase winding 2 to a source ofsupply LI, L2, L3 by way of a line switch it.

A contactor ii, having contacts l2, i3, i4, i6 and an operating coil [6,is employed to connect the single-phase winding 3 to the source L2, L3,through the line switch iii. A single-pole doublethrow contactor I! hascontacts l8 and IS, the selective closure of which is determined by acam 20 driven by the motor I through a speed reducer 2i. It is clearthat, normally, contacts l9 are closed while a follower pin 22 is inengagement with the outer periphery of the cam 20 responsive to the biasof a spring 24. However, when a rise 23 in the cam is reached by the follower, contacts is open and contacts i8 close.

A latch switch 25, having normally-open contacts 26, is so arrangedthat, when a handle 21 is pushed to close the contacts 26, as shown inthe solid lines of Fig. 1, against the bias of a spring 26, a latch 29operates to hold the contacts 26 closed until later released by a tripcam 30 which is driven by the motor I through the speed reducer 2|.

It is clear that the cam 20 and trip cam 30 may be preadjusted angularlyrelative to the events of the work cycle as set up for the machine 33 sothat the operator need only initiate each cycle by manually closing theswitch 25, the entire system ultimately coming to rest against apositive stop of the machine 39 with the power off, ready for the nextcycle.

In operation, assuming that the line switch is closed, manual closure ofthe switch 25 sets up the following circuit, from L2 through the coil 9,closed contacts l5, l9 and 26 to L3. This puts voltage on the coil 9,and contactor 5 operates to close contacts 6, I and 8, thus connectingthe winding 2 to the supply lines Ll, L2 and L3. The motor I thus comesup to speed and runs as a asiaaes polyphase induction motor at a speeddetermined by the number of poles in the Winding 2. Thus, the majorevents of the work cycle for the machine as may take place at fullspeed. Just prior to stopping the machine, the follower pin 22 isdisplaced by the rise 23 of the cam iii. The contacts l9 open and itclose. Opening of contacts i9 opens the circuit from L2 and L3 throughthe coil 9, and contactor 5 returns to its normallyonen position, thusdisconnecting the polyphase winding 2 from the line Ll, L2 and L3.Closure of contacts it completes a circuit from L2 through the coil l3,contacts is and 26 to L3. This puts voltage on the coil iii, and thecontactor ll operates to close contacts i2, i3 and it, and to opencontacts l5. Contacts i i are sealing contacts to maintain the circuitclosed after contacts in again open due to the rotation of the cam 29.

Operation of the contactor it puts a singlephase voltage from L2, L3 onthe winding 8. Since this winding has a larger number of poles than thewinding 2, the rotor will be running above the synchronous speeddetermined by the winding. 3 when the shift in windings is made. This isthe condition for induction generator action, and the stored rotationalenergy of the system is consumed in returning electrical energy to thesource L2, L3. This action is accompanied by a rapid slowing down orbraking of the motor until the motor is again driving the load, but nowat the slower speed established by the larger polenumber winding 3.

Foraaz to 1 ratio of pole-numbers, this slower a speed will beapproximately one-half the full speed of the system and thus the storedrotational energy has been decreased to about onequarter of its originalvalue and represents the maximum energy that must be absorbed tocompletely stop the machine. Thus, the mechanical shock sustained whenthe machine runs into the positive stop is greatly decreased by theaforesaid quick speed-reduction.

Just prior to the positive stop, the trip cam 30 releases the latch 29,as shown in. the dotted lines of Fig. 1 and opens the contacts 26 of theswitch 25. This opens the circuit through the coil l6 and the contactorI I returns to normal and disconnects the winding 3 from L2, L3,removing all voltage from the motor I Finally, a positive stop isreached, all motion ceases, and the system is returned to normal, readyfOr another cycle.

To assist in visualizing the torque-speed relations involved in thisoperation, referencr to Fig. 2 shows characteristic curve 3| for themachine 39 being driven, the curve 32 for the motor with winding 2 andthe curve 33 for the motor with the winding 3. Full load running speedoccurs at point 34. When the single phase winding 3 is switched in, themotor exerts a negative or braking torque, as at point 35, and the motorslows down rapidly due to the braking torque in the cross-hatched areaA. At the zero torque point 36, the motor again develops positive torqueand stable operating point 31 is reached. After this point, the winding3 is disconnected from time source L2, L3 and the motor runs into apositive stop. It will be seen that, even if the power is not removedfrom the motor before it reaches the stop, it cannot exert any drivingtorque at the stop because the single-phase winding 3 produces zerotorque at standstill, as indicated at point 38. S2 and S3 indicate thesynchronous speeds, respectively, of the motor windings 2 and 3.

A typical application for this system is in driving a group-stitchsewing machine in which a predetermined group oi stitches are made andthe machine then stopped. It is clear that. in order to provide themaximum useful working time, the times taken to accelerate anddecelerate the machine must be minimized and that, also, the maximumspeed must be as large as possible consistent with the ability of themachine parts to safely absorb the shock of stopping. As an indicationof the effectiveness of the system of this invention in a particulargroup-stitching appllcation, it has been determined that, ideally, if notime at all were allowed for acceleration and deceleration, 45 stitchescould be sewn per cycle whereas, actually, 42 stitches were sewn. Thisis expressed as an effectiveness of 42/45 or 93.4%.

This system according to the invention is not to be confused with thoseemploying conventional multi-speed motors having multi-phase windings ofdifl'erent pole numbers. In those systems both windings must providestarting torque and hence the simple single-axis winding employed herecannot be used. A further distinction resides in the fact that if aconventional multi-speed motor goes into stop position with the poweron, the mechanical shock is augmented by the substantial standstilltorque exerted, which, in the case of the system of this invention iszero.

Having thus set forth the nature of the invention, what I claim hereinis:

1. A system for controlling the operation of machines, comprising aninduction motor having a polyphase winding, a single-phase windinghaving a larger number of poles than said polyphase winding, a source ofpolyphase electrical energy, manually selective means for connectingsaid polyphase winding to said source of energy, automatic means fordisconnecting the polyphase winding from said source and connecting thesingle-phase winding to one phase of the source of energy, andmotor-operated means for disconnecting the single-phase winding after apredetermined number of revolutions of said motor.

2. A braking control system for an alternating current motor of theinduction type having a. squirrel cage secondary winding and twoseparate primary windings of different pole and phase numbers,comprising a source of energy, means for connecting the primary windingof lower pole number to said source, means for. subsequentlydisconnecting said lower-pole'number winding from and connecting theprimary winding of greater pole number to said source of energy, saidprimary winding of greater pole number being wound on a single-phaseaxis so as to provide zero torque at standstill.

3. A motor control system comprising in combination, an induction motorhaving two separate primary windings of different pole and phasenumbers, a source of electrical energy, manually operative means forconnecting the primary winding of lower pole numbers to said source,first means operative from said motor to disconnect said lower polenumber winding from, and to connect the higher pole number winding tosaid source after a. predetermined number of revolutions of said motor,and second means, operative from said motor subsequent to the operationof said first means, to disconnect the motor windings entirely from saidsource of energy, and third means comprising a'mechanical'stop forenergy, a polyphase primary winding, a'scparate single-phase primarywinding having more poles than said poiyphase winding, manuallyoperative means for connecting said polyphase winding to said source ofenergy for eifecting normal rotation of said motor, means responsive tosaid motor rol0 tation for disconnecting the polyphase winding from saidsource and connecting the single-phase winding to said source wherebythe speed of the motor is initially greater than the synchronous speeddetermined by the single-phase winding so that induction generatoraction takes place to brake the inertia load to a lower speed.

5. In a motor control system, a source of single frequency electricalenergy, an induction motor having a'closed-circuited secondary windingand two electrically insulated primary windings, the first of saidwindings being polyphase, the second oi said windings being single-phaseand having a larger number of poles than said polyphase winding,manually operative means to connect the polyphase winding to said sourcefor efiecting normal rotation of the motor, means responsive to therotation of said motor for disconnecting said polyphase winding fromsaid source and connecting said single-phase winding to said source, 80

and mechanical means for stopping the rotation of said motor while saidsingle-phase winding is connected to said source.

6. In a system of control for an electric motor,

a source of electrical energy, an induction motor .2

having two separate primary windings or different phase and polemnnbers, a cam driven by said motor, a first switch operated by saidcam, a manually closable switch provided with a latch for maintainingits closed position, a trip member driven by said motor Ior releasingsaid latch to open said manually closable switch, means responsive tothe closure of said manually closable switch for connecting one of saidwindings to said source, and means responsive to the operation of saidfirst switch for disconnecting said one of said windings and connectingsaid other one of the windings to said source.

7. In a braking system for a polyphase induction motor, a source ofelectrical energy, an induction motor having a closed-circuitedsecondary winding and a polyphase primary winding for eii'ecting normalrotation of said motor, a separate single-phase primary winding having alarger number of poles than said polyphase winding, means fordisconnecting said polyphase winding from said source during normalrotation of said motor, and means for simultaneously connecting saidsingle-phase winding to said source whereby said motor runs at a speedabove synchronism as determined by the single-phase winding and isbraked to a lower speed by the induction generator action thus produced.

HARRY B. FUGE.

REFERENCES CITED Number Name Date Werner Jan. 6, 1942' 2,388,009 Smith..s- Oct. 2, 1945

